Currents and Tides Help

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By — McGraw-Hill Professional
Updated on Sep 4, 2011


Ocean waters are constantly on the move. Currents flow in complex patterns affected by wind, salinity and temperature, bottom topography, and the Earth’s rotation.

Determined by forces such as wind, tides, and gravity, currents keep the oceans stirred up. Currents move water thousands of miles. There are many different currents, but the seven main currents include the Antarctic Circumpolar Current (also called the West Wind Drift ), East Wind Drift , North and South Equatorial currents , Peru Current , Kuroshio Current , and Gulf Stream . These currents move in large rotating circles called gyres .

Warm surface currents move from the equator to the higher latitudes, driven by atmospheric winds and the Earth’s rotation. Cold surface currents start out from polar and temperate latitudes, then move south toward the equator. Like the warm surface currents, they are driven mainly by atmospheric forces. Gyres form when the main ocean currents intersect. Water flows in a circular path: clockwise in the northern hemisphere and counterclockwise in the southern hemisphere.

Large ocean currents are driven by atmospheric winds that whip the planet all year round. The winds at the equator are called the northeast and southeast trade winds. At the mid-latitudes, the winds are called the westerlies, and at the highest latitudes, the winds are called the polar easterlies. These winds blow in the same direction all year.

The Antarctic Circumpolar Current and the Kuroshio Current are two of the largest currents. The Antarctic Circumpolar Current circles eastward around Antarctica, while the Kuroshio Current, located off Japan’s coast, travels up to 120km a day at a speed of nearly 5km/hr. A global circular current takes place when deep water is created in the North Atlantic, sinks, moves south, roams around Antarctica, and then heads northward to the Indian, Pacific, and Atlantic basins. Oceanographers estimate that it takes roughly a thousand years for water from the North Atlantic to wind its way into the North Pacific.

The California current is an eastern boundary current. It is wide, leisurely, cool, and shallow. Eastern boundary currents are frequently linked with upwelling.

The Somali current , off Africa’s eastern coast, is a current with a twist. It does the impossible, it reverses direction twice a year. From May through September, the Somali current runs northward. Then from November through March it runs southward. April and October must serve as the turnaround months, like the round house for trains. As the Somali current flows northward, upwelling takes place and brings nutrients to marine life. However, when the current turns southward again, the banquet table is put away and everybody goes back to work.

Most people have heard of the Gulf Stream. It has a strong effect on the East Coast of the United States. The Gulf Stream surface current is a strong, western boundary current. It is warm, deep, swift, and fairly salty, separating open ocean water from coastal water. Western currents move commonly from tropical to temperate latitudes. The Gulf Stream commonly travels at a speed of nearly 4 knots.

The Gulf Stream is part of a greater current system that includes the North Atlantic Current , Canary Current , and the North Equatorial Current . From the Yucatan Peninsula in Mexico, the Gulf Stream moves north through the Straits of Florida and up the east coast of Florida. When it gets to around North Carolina of the United States, it starts to slip off into the North Atlantic toward the Grand Banks near Newfoundland.

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